What is the Quetelet Index. (BMI)?

Body mass index, often referred to as simply BMI, is a numeric value calculated using an individual’s mass and height. A BMI may also be called a Quetelet index because the mathematician who developed this measurement scale was named Adolphe Quetelet. Quetelet’s premise was based on the idea that weight is relative to height, making it possible to calculate an ideal weight based on height. To calculate BMI, divide body mass by height squared.

Physicians and scientists disagree about some components of BMI due to its simplicity. BMI does not consider specific body composition and the muscle-to-fat ratio of an individual. Additionally, BMI correlates proportionally to weight and is inversely proportional to the height calculation. Thus, the BMI of tall people will be higher due to natural scalability. Taller people often have slighter body frames than shorter people, which would mean that they would have less body fat. However, BMI results for taller people may place them above the normal weight categories.

BMI is used to quantify the tissue mass present in a person. After performing the calculation, the BMI scale determines whether the person falls into one of five different categories, which are underweight, normal, overweight, obese, and severely obese. A BMI calculation of less than 18.5 would be underweight. The normal weight BMI numbers range between 18.5 and 24.9. Individuals with BMIs falling between 25 and 29.9 would be classified as overweight. When the BMI calculation ranges between 30 and 39.9, a person is classified as obese. Those with BMIs over 40 fall into the severely obese category. People with BMIs over the normal range may be at risk for health issues such as heart disease, diabetes, high blood pressure, and stroke. Additionally, people in Asian and black ethnic groups can be at risk of health issues at lower BMI levels, possibly experiencing health problems at BMIs as low as 23. Those with very low BMIs may also experience health problems because they are not ingesting sufficient nutrients and calories to maintain good health.

BMI calculations have limitations when it comes to determining the ratio of lean muscle mass to fat mass in people. It’s common for a person with a very high BMI to have a high percentage of body fat, but this is not always the case. Athletes with a high percentage of muscle mass will have a higher weight because muscle weighs more than fat. These individuals could have a BMI of over 25, placing them into the obese category, but they can in reality be very lean and healthy. In this case, a physician or other health care provider would need to recognize the disparity and would need to evaluate the athlete’s unique health status and any risks aside from the BMI calculation. Another potential limitation with BMI is with assessing weight in older individuals. As people get older, their muscle mass tends to decrease. This means that a person may have a normal BMI, but they actually have a body composition that is higher in fat and lower in muscle, which can be unhealthy. The BMI would not detect this higher fat ratio, which could be a health risk for older individuals.

Some researchers contend that measuring an individual’s waist circumference is a more accurate indicator of fat mass levels than measuring BMI. A larger waist circumference would indicate higher amounts of fat accumulating in the torso. Fat in the waist and chest is considered to be unhealthier than fat accumulation around the hips and thighs. Combining BMI calculation with measurement of the waist circumference may be a more accurate indicator of weight-related health risks.

Using BMI to assess weight is easy because the calculation only uses weight and height values. As a screening tool, BMI can be useful, as with this information, a physician can identify potential health risks. However, the limitations of BMI make it crucial to combine the results of the calculation with other diagnostic and screening tools to have complete information about health and possible future issues.

Online DNP Program